Infectious complications following Venetoclax-Proteasome Inhibitor based regimens in relapsed myeloma: a single center retrospective analysis

Abstract

using an in vivo splicing assay. These analyses identified SNVcluster that caused aberrant RHAMM splicing, thereby leading to increased RHAMM-V3 transcript expression. We have observed progressive overexpression of SF PTBP1/2 in MM patients and associated with disease progression. Since SNVs on the RHAMM modulate canonical SFs binding sites, we tested the effects of PTBPs deregulation on RHAMM splicing. We expressed PTBP1/2 in H929 cells, and then evaluated the RHAMM splicing pattern in transfected cells at a single cell (SC) level. SC analyses showed that overexpression of PTBP1/2 increased (2.5-fold) the RHAMM-V3/ FL ratio in MM cells. SC analyses also identified overexpression of RHAMM-V3 splice variant in 18% H929 SCs expressing PTBP1, and in 37% of cells expressing PTBP2. Our findings were confirmed at the SC level in different subpopulations of cells within relapsed MM patient BM samples overexpressing PTBP2. We also evaluated RHAMM splicing patterns and determined RHAMM-V3/ FL ratios. Our SC analyses suggested selective expression of RHAMM-V3 in marrow-infiltrating myeloid cells: 50% myeloid cells express RHAMM-V3 variant alone, and 79% PC express this variant in combination with RHAMM-FL. Moreover, RHAMM-V3/FL ratio in PC is elevated (2.6-fold), further confirming a correlation between the RHAMM variant ratio and clinical outcome. Conclusions: Our study suggests that aberrant RHAMM splicing in MM can result from SNPs/SNV affecting SRE, and due to the upregulation of PTBP1/2. Importantly, our study is the first to show RHAMMV3 variant associated with PTBP2 overexpression and identifies novel targets for RNA-based therapeutics. For example, overexpressed RHAMM-V3 in MM can be selectively targeted using an antisense oligonucleotide (ASO) based approach, thereby decreasing RHAMM-V3 production and improving MM patient outcome.Background: Multiple myeloma is an incurable haematological malignancy characterised by molecular complexity and clonal heterogeneity. Although both MCL-1 and BCL-2 are necessary for myeloma survival, most myelomas are dependent on MCL-1 such that BCL-2 inhibition alone only yields significant cytotoxicity in a minority of cases. Cooperative inhibition of both proteins may be beneficial. In the era of novel medicines and targeted molecular therapies, there is a shortfall of rapid and reliable assays that can predict patient response to new agents. This is particularly true in myeloma where primary samples survive poorly in vitro away from the bone marrow niche. We present a novel short-term biomarkerbased cytochrome c release assay capable of predicting long term sensitivity to MCL-1 and BCL-2 BH3-mimetics. This short term and reproducible assay can provide a quick response profile and mitigate the difficulty in culturing primary myeloma cells for long periods ex vivo. Method: Myeloma cell lines and CD138 selected primary samples were treated with venetoclax and S63845 alone and in combination. Sub-toxic doses of drugs were determined for each cell line. Samples were fixed after 4 hours d...